A review has been launched to establish if authorities could have acted sooner to prevent a primary school teacher sexually assaulting pupils as young as six, allegedly for more than a decade.

Nigel Leat was jailed indefinitely for abusing children he taught, often when other pupils were present, and secretly filming his attacks.

He groomed at least one girl a year at Hillside first school in Weston-super-Mare, Somerset and showered her with gifts, afforded her privileges and organised one-on-one teaching sessions.

Leat, 51, would swear his victims to secrecy and even write letters to them in which he would describe what he wanted to do to them and ask them to reply.

After the sentencing, North Somerset council revealed that the headteacher of Hillside, Chris Hood, had been suspended and an independent serious case review was being held.

A spokesman said: "This will examine the circumstances around what has happened and will help us answer the question on most parents' lips: 'Could action have been taken earlier that would have prevented abuse?' "

The spokesman said the headteacher was suspended after "concerns were raised about leadership and management" at the school.

"There is no police involvement in this process and no ongoing investigation of any other members of staff at the school."

Married father of two Leat, from Bristol, admitted 36 offences involving five pupils aged between six and eight over five years. The offences included sexual assault, attempted rape, voyeurism and possessing extreme pornography.

But police say they could have charged him with as many as 500 offences and believe he had been abusing children for 12 years.

About 30 parents and teachers watched at Bristol crown court as Judge Neil Ford QC, the recorder of Bristol, sentenced Leat to an indefinite term and ruled he must serve at least eight and a half years.

Leat would only be released when experts were sure he did not pose a risk to the public, he said.

The judge told Leat: "Your manipulation of the children was clever, cunning and insidious. It was also wicked.

"You were able to carry out repeated abuse. No members of staff or parents suspected that you were conducting this abuse."

Leat told a psychiatrist that he could not stop. "You said that you could think of nothing else other than taking a camera to school and making films. You described it as being an obsession," the judge said.

He said the victims were old enough to remember what had happened to them: "At some stage they will have to deal with the shame and depravation that you have brought upon them."

Outside court, the senior investigating officer, Detective Superintendent Geoff Wessell, said it was the "worst breach of trust" he had ever come across in his career.

He said he would support anyone else who came forward and said they had been abused by Leat.

The abuse went undetected at the school – where Leat taught for 15 years – until December last year when one victim told her mother that Leat had been touching her.

He was arrested within hours and officers found hundreds of films of his abuse stored on memory sticks in his classroom.

Leat, a former musician, keen birdwatcher and cyclist, qualified as a teacher in 1984 and only taught at Hillside.

He was warned in 2008 about being too "tactile" with the girls in his class as staff were worried that it might leave him open to accusations of improper behaviour. No further action was taken.

A parent once expressed concern about his behaviour after he asked a girl if she had a webcam so they could stay in touch after she left his classroom.

The concerns were not passed on to the authorities. Police were not alerted to worries over Leat until last December. The review is expected to be completed by the autumn.